9 Anastrozole (Arimidex) Side Effects and How to Manage Them

Anastrozole (Arimidex) is a common prescription medication that treats people living with early or advanced hormone receptor-positive breast cancer. It’s usually only taken by women who have gone through menopause.

Anastrozole comes as an oral tablet, and it belongs to a class of medications known as aromatase inhibitors (AIs). Aromatase is a natural protein that converts hormones to estrogen in the body. Hormone receptor-positive breast cancer relies on estrogen as fuel to grow, so by blocking aromatase, anastrozole lowers the amount of estrogen in the body. This can help suppress further cancer growth.

While anastrozole is beneficial for fighting cancer, it can also cause side effects — especially ones related to fluctuating estrogen levels in the body. Since anastrozole is recommended to be taken for at least 5 years or more, it's important to know how to manage possible side effects.

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Anastrozole (Arimidex) side effects at a glance

So, what are the major side effects of anastrozole? These are the top ones to look out for.

Common anastrozole side effects include:

• Hot flashes

• Nausea

• Vomiting

• Muscle, joint, and bone pain

• Fatigue

• Changes in mood

• Vaginal bleeding

• Vaginal dryness

• Swelling

• Headaches

• Insomnia

Rare but serious side effects include:

• Weaker bones (osteoporosis)

• High cholesterol

• Heart problems

Read on to learn more about nine noteworthy anastrozole side effects and how to manage them.

1. Hot flashes

If you’ve gone through menopause, you’re probably familiar with the unpleasant feeling of heat rushing to your face, neck, or chest. Or the sweating, chills, and feelings of anxiety that can come along with it. Anastrozole can cause hot flashes like those experienced during menopause.

About 36% of people with early-stage breast cancer who took anastrozole in initial studies reported experiencing hot flashes. Hot flashes happen because of how anastrozole affects estrogen in the body, which plays a role in regulating your body temperature.

Thankfully, there are many ways to manage hot flashes if you experience them while taking anastrozole. You can try medication-free remedies, such as wearing loose-fitting clothing and keeping stress levels low with relaxation techniques. And to help prevent hot flashes in the first place, some foods to avoid when taking anastrozole include:

• Spicy foods

• Caffeinated beverages

• Alcohol

Staying well-hydrated and quitting smoking doesn’t hurt either.

If hot flashes ever become unmanageable, reach out to your cancer specialist. There are medications that can help. Antidepressants and clonidine are two examples. You could also ask about switching to another treatment that causes fewer hot flashes. And try to avoid hot flash supplements unless your cancer specialist gives you the OK — these products can cause problems in certain situations.

2. Nausea, vomiting, and stomach upset

Nausea, vomiting, and upset stomach are common side effects of anastrozole too.

Taking anastrozole with food can lower your risk of developing nausea. But if you end up feeling nauseous, eating bland foods such as saltine crackers or broth can help. Avoiding nausea trigger foods when taking anastrozole can also help. This includes spicy, acidic, and greasy foods.

Gastrointestinal symptoms should go away as your body adjusts to the medication. But if your nausea doesn’t improve over time, talk with your cancer specialist about anti-nausea medications that may be able to offer relief. If nausea or vomiting becomes so severe that you aren't able to keep fluids down, let your cancer specialist know right away.

3. Muscle and joint pain

Another common side effect of anastrozole is muscle and joint pain. About 36% of people with early-stage breast cancer who took anastrozole experienced joint problems in initial studies. People often experience morning stiffness or joint pain in the hands, knees, and/or back. Joint pain usually starts about 2 months or longer after starting an AI like anastrozole.

It's not exactly known why anastrozole causes muscle and joint pain. But it's thought to be related to the sudden drop in estrogen levels that this medication can cause. Additionally, joint aches and pains are also common during menopause due to lowering estrogen levels.

To combat these symptoms, try partaking in regular exercise to promote joint mobility and muscle strength. Massage therapy and losing weight (if you have overweight) can also help lessen muscle and joint pain. OTC pain relievers, such as ibuprofen (Advil, Motrin) and acetaminophen (Tylenol), can offer temporary relief when needed.

If you’re still experiencing pain after trying measures like these, let your cancer specialist know. They may recommend other management options, such as taking omega 3 and vitamin D supplements, or switching to different AI.

4. Feeling tired or moody

Lower amounts of estrogen in the body may affect your mood and energy levels. Nearly 20% of people taking anastrozole for early-stage breast cancer reported some changes in mood or tiredness.

If you experience mood changes or excessive fatigue after starting anastrozole, talk to your cancer specialist about ways to cope. They may recommend natural remedies, such as mindfulness techniques, exercise, or counseling to help improve your mood. In more substantial cases, they may suggest taking an antidepressant or switching to another treatment that has less mood-related effects.

5. Vaginal bleeding and dryness

Anastrozole may occasionally cause vaginal bleeding and dryness. Vaginal bleeding and dryness happen as a result of anastrozole’s estrogen-lowering effects.

If you have vaginal dryness, you can try OTC vaginal moisturizers or lubricants. If you need additional relief, you can also ask your cancer specialist about low-dose, estrogen-containing vaginal products for dryness.

Vaginal bleeding can happen when you first start taking anastrozole, but this tends to resolve over time. If you have abnormal vaginal bleeding or bleeding that doesn’t go away, let your cancer specialist know right away.

6. Swelling

Swelling due to fluid buildup in the feet, ankles, and arms is another possible anastrozole side effect.

To lower your chances of swelling, do your best to avoid standing for long periods of time. You can also try wearing compression socks and elevating your feet from time to time. Limiting the amount of salt and processed foods in your diet may also help.

If swelling becomes painful or severe, let your cancer specialist know right away. And if you have sudden chest pain, shortness of breath, or a dry cough, get immediate medical help. This may be a sign of fluid around your lungs, which is a medical emergency.

7. Weaker bones

Anastrozole can potentially cause your bones to thin and weaken over time — especially when taken for 2 years or more. This long-term side effect of anastrozole raises your risk of fractures and a condition known as osteoporosis.

Anastrozole causes your bones to thin because it blocks estrogen. Estrogen is important for maintaining bone health. Because of this, your cancer specialist may periodically recommend a bone density test to monitor your bone strength while taking anastrozole.

Other ways to help maintain strong bones while taking anastrozole include taking a bone-strengthening medication such as zoledronic acid (Reclast) or denosumab (Prolia). These medications can help prevent bone loss. Your cancer specialist may also recommend taking vitamin D and calcium supplements to support bone health.

8. High cholesterol

Anastrozole can raise your cholesterol levels. In initial studies, about 9% of women who took anastrozole had higher cholesterol levels compared to about 4% of people who took tamoxifen (a different breast cancer medication).

Having high cholesterol can raise your risk of heart problems over time, including heart attacks or strokes. This is another one of the long-term side effects of anastrozole. Your cancer specialist will likely want to check your cholesterol levels routinely while taking anastrozole.

9. Heart problems

It’s less common, but anastrozole can raise your risk for heart disease. This can include problems such as heart failure, chest pain, and heart attacks. It's not entirely understood how anastrozole raises your risk of heart problems. But it may be related to higher cholesterol levels.

Your risk of heart problems while taking anastrozole may be higher if you have a history of heart problems. Let your cancer specialist know if you have a history of heart problems. They may suggest another hormone therapy to treat your breast cancer.

Anastrozole side effects in women vs. men

Anastrozole is mainly used to treat hormone-receptor positive breast cancer in women. But it’s rarely used to treat male breast cancer. What’s more, some men take anastrozole off-label to help address fertility issues by increasing the quality and quantity of sperm.

The side effects of anastrozole are similar between men and women, but there are some exceptions. This is because anastrozole’s estrogen-lowering effects may affect men and women differently.

Women may experience side effects such as vaginal dryness or bleeding. In turn, men are more likely to develop a reduced sex drive. Both men and women can experience bone loss, but it’s more likely to happen in women.

When should you contact your cancer specialist about anastrozole side effects?

Listening to your body is important, especially when it comes to taking anastrozole. You should let your cancer specialist know if you have any side effects that you can't tolerate. They can help you find ways to manage the side effects of anastrozole since it’s recommended to be taken for at least 5 years.

If you experience any of the following serious side effects, you should let your care team know right away — they may be signs of a medical emergency:

• Heavy vaginal bleeding

• Sudden chest pain

• Shortness of breath

• Lightheadedness

• Dry cough

• Painful or severe swelling

How to save on anastrozole

There are ways to save on Arimidex, which is available as a generic- and brand-name medication. GoodRx can help you navigate between GoodRx coupons and copay savings cards to save money on your prescription.

• Save with GoodRx: Anyone with a valid prescription, regardless of insurance status, can use GoodRx to purchase a 30-day supply of Arimidex at an exclusive cash price of $298.80. You can also pay as little as $9.74 for an equivalent supply of the generic.

• Save with a copay savings card: If you have insurance, you may be eligible to pay as little as $60 (30-day supply) or $180 (90-day supply) for Arimidex using the manufacturer’s Arimidex Patient Direct program. This program also offers home delivery.

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Written by:

Vanessa Carranza, PharmD

Vanessa Carranza, PharmD, is a pharmacist who has dedicated her career to the advancement of medical education for healthcare providers, patients, and caregivers, most notably in the oncology space.

Edited by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

Reviewed by:

Amy B. Gragnolati, PharmD, BCPS

Amy Gragnolati, PharmD, BCPS, is a pharmacy editor for GoodRx. Amy currently holds her pharmacist license in Georgia and California.

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